fix: create directory recursive to prevent failures with existing directories

Author: salzig

.travis.yml

@@ -4,7 +4,7 @@ env:
   - PATH=$HOME/bin:$PATH
 install:
   # install newer phantomjs, see https://github.com/travis-ci/travis-ci/issues/3225 for discussion
-  - mkdir $HOME/bin
+  - mkdir -p $HOME/bin
   - curl https://s3.amazonaws.com/travis-phantomjs/phantomjs-2.0.0-ubuntu-12.04.tar.bz2 | tar Oxjv phantomjs > $HOME/bin/phantomjs
   - chmod +x $HOME/bin/phantomjs
   - scripts/setup